He had been one of 10 Patriots players listed as questionable for Sunday's game, but the Patriots on Saturday night officially downgraded him to doubtful.
Gronkowski, who has a history of back ailments, has been dealing with ankle trouble this season that has landed him on injury reports and limited his practice participation, but his back injury was just added to the injury report yesterday.
Under Bill Belichick, the Patriots have never lost three consecutive road games to begin a season.
But the Pro Bowl tight end has not been ruled out yet.
Davis and Schwenke are the only heathy inactives.
Mack suffered the ankle injury in the first half of the loss to the Dolphins last week, but he played through it in the second half.
- Cole Croston will be the top backup offensive tackle behind left tackle Trent Brown and right tackle LaAdrian Waddle, who will take over for Cannon. Fullback Michael Burton, outside linebacker Kylie Fitts, offensive linemen Rashaad Coward and Bryan Witzmann, wide receiver Javon Wims and defensive lineman Nick Williams were healthy scratches for the Bears.